# class Stack:
#     def __init__(self):
#         self.items = []
#
#     def isEmpty(self):
#         return self.items == []
#
#     def push(self, item):
#         self.items.append(item)
#
#     def pop(self):
#         return self.items.pop()
#
#     def peek(self):
#         return self.items[len(self.items) - 1]
#
#     def size(self):
#         return len(self.items)
